An applicator includes a piston plate, a non-linear coil spring, a casing, a lock means and a release means. The casing includes a tubular main body part that houses therein the piston plate and the non-linear coil spring, and a cover part that is arranged on one end side of the main body part. The cover part and the piston plate sandwich the non-linear coil spring there between. The lock means locks the piston plate with the casing such that the piston plate is held at a retraction position thereof on the cover part side in a state where the cover part and the piston plate compress the non-linear coil spring. The release means releases a locked state where the piston plate is locked with the casing by the lock means and where the cover part and the piston plate compress the non-linear coil spring.